Vibratory sifting machine with strikers

ABSTRACT

A sifting machine composed of a sheet of perforate screening material clamped in place only along its front and rear edges relative to the direction of conveyance therealong of material being sifted, and vibration producing means composed of a plurality of strikers arranged to undergo rotary oscillatory movement and to stroke the lower surface of the screening sheet, the strikers being driven by driven shafts, each shaft carrying several strikers, to which are imparted pivotal oscillatory movements under the influence of one or several oscillatory drives.

United States Patent r1 1 Krause [111 3,796,311 [451 Mar. 12, 1974 VIBRATORY SIFTING MACHINE WITH STRIKERS [75] Inventor: Rudolf Krause,

I l-lomburg-Dornholzhausen, Germany [22] Filed: I Feb. 24, 1971 [21] Appl. No.: 118,413

[30] Foreign Application Priority Data Feb. 24, 1970 Germany 7006692 [52] US. Cl 209/275,209/347, 209/382 [51] Int. Cl B071) 1/34 [58] Field of Search 209/349, 310, 368, 322, 209/379, 381, 382, 347, 346, 275, 276

[56] References Cited UNITED STATES PATENTS 3,616,905 11/1971 Kristek 209/310 3,225,926 12/1965 Dostatni 209/368 X 3,370,706 2/1968 Bruninghaus. 209/368 3,630,356 12/1971 Isaacson 209/368 133,662 12/1872 Mowry 209/382 694,444 3/1902 Thurmond 209/382 X 959,671 5/1910 Willson 209/347 1,380,289 5/1921 Childers 209/382 X 1,456,801 5/1923 Hoyle 209/310 1,904,032 4/1933 Roberts 209/382 X 2,053,895 9/1936 Burmeister 209/382 X 2,279,225 4/1942 Cecil 209/382 2,443,543 6/1948 Peterson 209/382 3,070,230 12/1962 Peterson 209/310 3,179,251 4/1965 Nickel 209/347 X FOREIGN PATENTS OR APPLICATIONS 38,913 5/1886 Germany 209/320 54,678 3/191 1 Switzerland... 115,327 11/1899 Germany 209/382 518,185 2/1940 Great Britain 209/310 219,841 12/1968 U.S.S.R......... 209/322 411,203 7/1945 Italy 209/382 1,041,332 10/1958 Germany 209/329 Primary ExaminerRobert Halfer Attorney, Agent, or Firm-Spencer & Kaye [5 7 ABSTRACT A sifting machine composed of a sheet of perforate screening material clamped in place only along its front and rear edges relative to the direction of conveyance therealong of material being sifted, and vibration producing means composed of a plurality of strikers arranged to undergo rotary oscillatory movement and to stroke the lower surface of the screening sheet, the strikers being driven by driven shafts, each shaft carrying several strikers, to which are imparted pivotal oscillatory movements under the influence of one or 1 several oscillatory drives.

7 Claims, 10 Drawing Figures PATENTEB MR 1 2 I874 SHEET 1 HF 3 FIG/I INVENTOR Rudolf Krouse and ATTORNEYS.

PATENTEU MR 12 I974 INVENTOR Rudolf Krouse ATTORNEYS.

PMENTED MR 1 2 m4 SHEET 3 0F 3 FIG.'+

INVENTOR Rudolf Krause M a "I; 313'.

1 VIBRATORY SIFTING MACHINE WITH STRIKERS BACKGROUND OF THE INVENTION The present invention relates to sifting machines, and particularly to machines whose screening member is clamped in place along its edges and can be excited directly be means of beaters.

In known sifting machines of this type the screening member is directly excited by means of a plurality of electromagnetic drives which are at least approximately uniformly distributed above the screening member and which act on the screening member via a striker fastened to the member and extending at right angles to the surface of the screening material constituting the member.

With these sifting machines there exists the drawback, however, that a plurality of drives is necessary. Moreover, the screening material must be provided with holes for the connection of the strikers. As a result, there is the danger that the screening material will be destroyed as a result of tears or breaks originating at those holes. 1

SUMMARY OF THE INVENTION It is a primary object of the present invention to overcome the above drawbacks and difficulties.

A further object of the invention is to simplify the structure of machines of the above-described type.

Another object of the invention is to reduce the incidence of breakdowns in such machines.

Still another object of the invention is to improve the output of such machines.

A specific object of the present invention is to provide a sifting machine of the above-mentioned type which is an improvement over prior art machines in that it employs less complicated drives, gives the screening member a longer service life, and produces a better sifting output.

These objects are achieved, according to the present invention, in that shafts are disposed below the screening material surface and are arranged to undergo rotary oscillatory vibrations, and a plurality of beater levers extend from the shafts to act as strikers, which beater levers coincide with the lower surface of the screening material.

This results in an extremely sturdy sifting machine in which each shaft operates a plurality of screening material strikers. Perforations are no longer required in the screening material. Moreover, the point-type attack of the strikers is retained, it being known that this results in the initiation of vibrations of the screening material which expand in a circle from each impact point and lead to good sifting results.

For a further increase in the sifting output and the service life of the screening, or sifting, material, an advantageous feature of the present invention resides in that the shafts are disposed to be transverse to the conveying direction of the sifting machine and, preferably, the screening material is clamped in a sieve frame only at the frontal and rear edges with respect to the conveying direction.

According to a further feature of the invention, the shafts are mounted through the intermediary of rubber torsion springs. This results in an almost maintenance free mounting of the shafts. Moreover, the elasticity of the rubber torsion springs causes harmonics to be superimposed on the oscillations of the shafts, and thus of the screening material, and this leads to still better sifting results than heretofore possible, particularly in the case of very finely granulated materials.

One form of construction of embodiments of the present invention, which is particularly favorable in that it simplifies assembly of the machine and increases the effectiveness of thedevice, consists in that the shafts and preferably also their drives are carried by the sieve frame of the machine.

Another advantageous embodiment which is easyto manufacture is one in which the shafts are coupled, via levers extending therefrom, with drives which perform linearly oscillatory movements, preferably with electromagnetic drives.

A variation of the above embodiment which might be preferred under certain circumstances is one in which the shafts are coupled with the rotating drive shafts of motors via crank drives engaging the levers.

A further modification according to the invention is one in which inertial mass drives which rotate on the shafts are provided and have rotating shafts oriented parallel to the shafts.

According to an advantageous further development, the strikers acting on the screening material oscillate at different frequencies and at amplitudes which may also vary from striker to striker.

In one specific preferred arrangement, at the input side of the inclined screening material the strikers oscillate at a lower frequency than at the output side while the amplitudes at the input side are greater than at the output side.

This preferred embodiment produces an entirely novel and surprising sieve effect in that at the input end of the machine there are far-reaching vibrations which act above the material then being sifted on the as yet unsifted material, these vibrations having a high amplitude normal to the screening material surface and being increasingly damped toward the output side, whereas at the output side higher frequency vibrations are imparted to the screening material and have low amplitudes normal to the screening material surface, these vibrations becoming weaker toward the input side. The closer the material to be sifted moves to the output side, the more rapid become the vibrations acting on the screening material and on the material to be sifted, These vibrations may even be combined with superimposed high-frequency vibrations imparted from an armature abutment of the electromagnet, so that the sifting action becomes more complete. The waves of the vibrations here run in respectively opposite directions and are superimposed at the screening material surface so that very high accelerations are imparted to the screening material surface which lead to an extraor dinarily high separation effect with an associated high throughput.

As a further simplification of the above-described arrangement, the shafts bearing the strikers are provided in groups each having a common drive, or all the shafts are coupled together, for example via a push rod, to a common drive.

Another specific arrangement according to the invention, which may be preferredunder certain circumstances, is one in which the movements of the beater levers are inclined to the screening material, and directed toward the input end thereof, when the screening material is struck This causes the time during which the material to be sifted remains on' the inclined screening material to be lengthened so that even material which is difficult to separate, e.g., which tends to stick together, can be sifted better than before.

To further improve the sifting output, an advantageous feature of the invention resides in that all of the heaters are arranged so that the portions which coincide with the screening material are disposed on an upwardly convex plane, the greater height of the central beater with respect to the beaters disposed near the edges preferably corresponding to the amount .by which the screening material sags in each respective zone. In this manner the distribution of material to be sifted over the entire surface of the screening material is further improved.

According to a further feature of the invention, and for increasing the effectiveness of the machine, each of thelevers is provided with bearing pins which are disposed eccentrically, and parallel, to the shaft axis, the bearing pins being mounted in the torsion springs. This makes it possible with simple means to balance the shafts carrying the levers so that the shafts and their drives can be made lighter. 1

A variation which might be preferred under certain circumstances is one in which counterweights are mounted on the shafts approximately diametrically opposite the beater levers.

To protect the screening material it is moreover advantageous to convexly curve the beater lever surfaces which contact the screening material.

For further increasing the output and the life mainly of the screening material of-the above-described sifting machines, the beater levers carried by each vibrating shaft can be bridged by a common ledge which is provided, atleast on the side facing the underside of the screen, with a coating of elastic abrasion resistant material.

Due to the inherent resonance of such coatings, high frequency harmonics are produced when the sieve is started which, inter alia, considerably improve the degree to which material is sifted out. At the same time the sieve is protected and its life expectancy is increased.

A preferred embodiment of the invention is one in which the beater levers of a vibrating shaft are bridged with a common ledge which is provided, at least on the side facing the underside of the sieve, with such a coating of an elastic abrasion resistant material.

It may be particularly advantageous under certain circumstances if the ledge according to the present invention is provided with a plurality of coatings of an elastic, abrasion-resistant materialwhich are spaced from one another parallel to the shaft.

According to a further advantageous feature of the invention, the elastic coatings at the ledge are mounted, at least in the direction of its longitudinal extent, to be displaceable and fixable.

In this connection, an advantageous embodiment is one in which setting members such as rods engage the coatings which are mounted on the vibrating lever ledge to be displaceable and fixable thereon, the setting members protruding beyond the sieve frame. This enables the strike zones to be varied in a previously unattainably rapid and easy manner.

A further advantageous feature of the invention resides in the elastic coatings being connected with the vibratory lever ledge by means of a plug-in connection which is secured at least by friction, preferably in such a manner that the elastic coatings are formed as grooved profile rods which enclose the vibratory lever ledge.

A variation of the above, which may be preferred under certain circumstances, is characterized in that the vibratory levers which are borne by a common vibrating shaft are bridged in groups by a common ledge which bears elastic coatings. It may here be of particular advantage if the elastic coatings are unremovably fastened to the vibratory lever ledges, for example by means of glue.

Finally, an advantageous feature for increasing the resonance is distinguished in that the vibratory levers are elastic, preferably in that the vibratory levers consist of rubber or rubber-like material or are at least resiliently mounted at the shafts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, with the side of the housing box and frame removed, of a sifting machine representing one embodiment of the invention.

FIG. la is a side elevational detail view of a modified form of construction of the embodiment of FIG. 1.

FIG. lb is'a view similar to FIG. 1a of another modified form of construction.

FIG. 1c is a view similar to FIG. la of a further modified form of construction.

FIG. 2 is a detail view, to an enlarged scale, of a portion of the structure of FIG. 1.

FIG. 3 is a plan view of the sifting machine in the direction of arrow-3 of FIG. 1.

FIG; 3a is a cross-sectional plan, detail view of an element of the embodiment of FIGS. 1-3.

FIG. 4 is a view similar to that of FIG. 1 of a further embodiment of the invention.

FIG. 5 is a detail elevational view, partially in cross section and to an enlarged scale, of the portion enclosed in circle B in FIG. 4.

FIG. 6 is a plan view, similar to that of FIG. 3, of the machine of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the machine of FIGS. 1-3, the sifting material member 1 is clamped into a sieve frame 2 only in the area of the front and rear edges relative to the conveying direction, a housing box 3 being connected below the frame 2 Below the screening material 1 four shafts 4 are disposed which are mounted on the sieve frame by .means of known rubber torsion springs 18, shown for only one shaft. These rubber torsion springs each consist of two concentrically disposed metal sleeves which have different diameters and between which a rubber ring is of a ring of an elastic synthetic material which has approximately the same elastic properties as rubber. The smaller diameter metal sleeve is fastened to shaft 4 and the larger diameter metal sleeve is fastened to the sieve frame.

From each shaft 4 five beater levers 5 extend, each lever carrying a convexly curved head 6. Outside of the sieve frame 2 an electromagnetic drive 7 is mounted for each shaft 4 and includes a linearly movable striker 8 joined to a lever 9 extending from, and rigidly connected to, shaft 4. As can be seen in FIGS. 2 and 3a, each end of each shaft 4 carries an eccentrically disposed bearing pin 10 which extends parallel to the axis of the shaft, the bearing pins rather than the shafts being mounted in springs 18. Under certain circumstances two or more of these shafts 4 may be suitably coupled and may have a common drive 7, as shown in FIG. la. Shafts 4 may also be provided with counterweights 1 1.

In the sifting machine shown in FIGS. 4-6 which is substantially similar to that shown in FIGS. 13, each row of heads 6 is replaced by a ledge 6' provided with elastic coatings 12 of an abrasion resistant synthetic, for example of polyurethane. Electromagnetic drives 7 act on shafts 4 to impart thereto a cyclically alternating torque which causes them to undergo an oscillatory, small angle rotation.

As can be seen in FIG. 6, the ledges 6 may be provided with a plurality of elastic coatings 12 which are spaced from one another along the length of the ledges. The coatings preferably have the form of an inverted trough which can be clamped around the ledges 6', as shown in FIG. 5.

FIG. 4 also shows, at 7, another embodiment of a drive according to the invention consisting of a rotary motor whose output shaft carries a crank for driving the associated rod 8, the latter being pivotally connected to lever 9.

In both illustrated embodiments, the drives can be constructed and controlled to produce the previously described varying oscillation amplitudes and frequencies.

FIG. lb shows a modified arrangement in which the composed of an inertial unbalance mass rotating on a shaft oriented parallel to shafts 4.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

I. In a sifting machine including: a sieve frame; a screening member constituted by a sheet of screening material clamped to the sieve frame and arranged to be vibrated for conveying material in a given direction along the screen surface; a plurality of shafts disposed below the screening material surface and having their axes oriented transverse to the given conveying direction, the shafts being mounted to the sieve frame to continuously undergo rotary oscillatory vibratory movements about their axes; and a plurality of strikers located beneath, and distributed across the entirety of, the surface of the screening material and operatively associated with the shafts to be driven thereby to didrive system is arranged so that the movements of I disposed near the edges corresponding to the amount by which the screening material sags in the region of each beater lever. FIG. It further illustrates an arrangement in which all of the shafts'4 are coupled together, via a push rod, to a common drive 7" which is rectly strike, and thus induce vibrations in, the screening material; the improvement wherein: said screening member is fastened, and supported, only at its front and rear edges with respect to the given conveying direction; and said strikers are combined into groups spaced apart in the conveying direction with each group being associated with at least one respective shaft, and the at least one shaft for each said group of strikers has a common drive for causing each said group of strikers to strike said screening material at a respectively different frequency.

2. An arrangement as defined in claim 1 wherein said shafts are mounted to said frame through the intermediary of rubber torsion springs.

. 3. An arrangement as defined in claim 1 wherein said groups of strikers are driven to oscillate at respectively different amplitudes.

4. An arrangement as defined in claim 3 wherein said groups of strikers at the input side of said machine, with respect to the conveying direction of material to be sifted, oscillate at a lower frequency and higher amplitude than said groups of strikers at the output side.

5. An arrangement as defined in claim 1 wherein the portions of said strikers which come into contact with said screening material are disposed on an upwardly convex plane.

6. An arrangement as defined in claim 5 wherein the locus. of said strikers defines an upwardly convex plane, with the height of each said striker corresponding approximately to the amount of sag of said screening material in the zone of contact of the respective striker.

7. An arrangement as defined in claim 1 further com prising a plurality of beater levers of elastic material mounted on said shafts for oscillatory movement therewith, with each said striker being mounted at the free end of a respective beater lever. 

1. In a sifting machine including: a sieve frame; a screening member constituted by a sheet of screening material clamped to the sieve frame and arranged to be vibrated for conveying material in a given direction along the screen surface; a plurality of shafts disposed below the screening material surface and having their axes oriented transverse to the given conveying direction, the shafts being mounted to the sieve frame to continuously undergo rotary oscillatory vibratory movements about their axes; and a plurality of strikers located beneath, and distributed across the entirety of, the surface of the screening material and operatively associated with the shafts to be driven thereby to directly strike, and thus induce vibrations in, the screening material; the improvement wherein: said screening member is fastened, and supported, only at its front and rear edges with respect to the given conveying direction; and said strikers are combined into groups spaced apart in the conveying direction with each group being associated with at least one respective shaft, and the at least one shaft for each said group of strikers has a common drive for causing each said group of strikers to strike said screening material at a respectively different frequency.
 2. An arrangement as defined in claim 1 wherein said shafts are mounted to said frame through the intermediary of rubber torsion springs.
 3. An arrangement as defined in claim 1 wherein said groups of strikers are driven to oscillate at respectively different amplitudes.
 4. An arrangement as defined in claim 3 wherein said groups of strikers at the input side of said machine, with respect to the conveying direction of material to be sifted, oscillate at a lower frequency and higher amplitude than said groups of strikers at the output side.
 5. An arrangement as defined in claim 1 wherein the portions of said strikers which come into contact with said scReening material are disposed on an upwardly convex plane.
 6. An arrangement as defined in claim 5 wherein the locus of said strikers defines an upwardly convex plane, with the height of each said striker corresponding approximately to the amount of sag of said screening material in the zone of contact of the respective striker.
 7. An arrangement as defined in claim 1 further comprising a plurality of beater levers of elastic material mounted on said shafts for oscillatory movement therewith, with each said striker being mounted at the free end of a respective beater lever. 